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class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Observable 与 RxJS" aria-pressed="false"><span>Observable 与 RxJS</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/observables" title="" target="_self"><span>可观察对象(Observable)</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/rx-library" title="" target="_self"><span>RxJS 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collapsed ng-star-inserted" title="Angular 中的模块" aria-pressed="false"><span>NgModules</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodules" title="使用 NgModule 让你的应用更高效" target="_self"><span>NgModule 简介</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodule-vs-jsmodule" title="JavaScript 模块和 NgModule 之间的差异" target="_self"><span>JS 模块 vs NgModule</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/bootstrapping" title="告诉 Angular 如何在根 &quot;AppModule&quot; 中构造和引导应用。" target="_self"><span>应用的根模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/frequent-ngmodules" title="介绍最常用的 NgModule" target="_self"><span>常用模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/module-types" title="介绍特性模块的几种类型" target="_self"><span>特性模块的分类</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/entry-components" title="关于 Angular 中入口组件的一切" target="_self"><span>入口组件</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/feature-modules" title="创建特性模块，以组织你的代码" target="_self"><span>特性模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/providers" title="服务提供者与 NgModule" target="_self"><span>服务提供者</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/singleton-services" title="创建单例服务" target="_self"><span>单例服务</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/lazy-loading-ngmodules" title="惰性加载模块，以提高应用的性能" target="_self"><span>惰性加载的特性模块</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/sharing-ngmodules" title="共享 NgModule 让你的应用现代化。" target="_self"><span>共享 NgModule</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodule-api" title="理解 NgModule 的那些细节。" target="_self"><span>NgModule API</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ngmodule-faq" title="回答关于 NgModules 的常见问题。" target="_self"><span>NgModule 常见问题</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="依赖注入：创建并注入各种服务。" aria-pressed="false"><span>依赖注入</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dependency-injection" title="Angular 的依赖注入系统能够为 Angular 创建的类创建并交付它们所依赖的服务。" target="_self"><span>Angular 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level-3 collapsed ng-star-inserted" style="position:relative" href="guide/dependency-injection-navtree" title="使用注入器树来查找父组件。" target="_self"><span>浏览组件树</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/http" title="通过 HTTP 协议与远程服务器对话。" target="_self"><span>HttpClient</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/router" title="揭示如何通过 Angular 路由进行基本的屏幕导航。" target="_self"><span>路由与导航</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Angular 动画系统指南" aria-pressed="false"><span>动画</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/animations" title="Angular 动画的基础技术。" target="_self"><span>简介</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/transition-and-triggers" title="转场与触发器的高级技术。" target="_self"><span>转场与触发器</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/complex-animation-sequences" title="复杂的 Angular 动画序列。" target="_self"><span>复杂序列</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/reusable-animations" title="创建可复用的动画。" target="_self"><span>可复用动画</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/route-animations" title="为路由提供转场动画。" target="_self"><span>路由转场动画</span></a></div></aio-nav-item></div></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="把 Angular 用到你的实际工作中的一些技巧" aria-pressed="false"><span>其它技术</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/security" title="Angular 应用开发中的安全技术。" target="_self"><span>安全</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/i18n" title="把应用模板中的文本翻译成多种语言。" target="_self"><span>国际化（i18n）</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/accessibility" title="设计能被所有用户访问的应用" target="_self"><span>无障碍（a11y）</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="Angular Service Worker: 控制应用资源的缓存。" aria-pressed="false"><span>Service Worker 与 PWA</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-intro" title="Angular 对 Service Worker 的实现提升了慢速或不稳定的网络连接下的用户体验。" target="_self"><span>简介</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-getting-started" title="在 CLI 项目中启用 Service Worker，并在浏览器中查看效果。" target="_self"><span>快速上手</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/app-shell" title="在 CLI 项目中启用应用外壳。" target="_self"><span>应用外壳</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-communications" title="那些能让你和 Angular 的 Service Worker 通讯的服务类。" target="_self"><span>与 Service Worker 通讯</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-devops" title="使用 Service Worker 运行应用、管理应用更新、调试以及杀掉正在运行的应用。" target="_self"><span>生产环境下的 Service Worker</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/service-worker-config" title="配置 Service Worker 的缓存行为。" target="_self"><span>Service Worker 配置</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/universal" title="使用 Angular Universal 在服务端渲染 HTML。" target="_self"><span>服务端渲染</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="把 AngularJS 应用增量式的升级到 Angular。" aria-pressed="false"><span>从 AngularJS 升级</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/upgrade" title="把 AngularJS 应用增量式的升级到 Angular。" target="_self"><span>升级步骤</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/upgrade-performance" title="用更灵活的方式把 AngularJS 升级到 Angular。" target="_self"><span>更关注性能的升级方式</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/ajs-quick-reference" title="学习如何把 AngularJS 的概念映射到 Angular 中。" target="_self"><span>AngularJS 与 Angular 的概念对照</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="使用共享库扩展 Angular" aria-pressed="false"><span>开发 Angular 库</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/libraries" title="理解何时以及如何使用和创建库。" target="_self"><span>库概览</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/using-libraries" title="把已发布的库集成进你的应用中。" target="_self"><span>使用已发布的库</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/creating-libraries" title="通过创建、发布和使用你自己的库来扩展 Angular。" target="_self"><span>创建库</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="理解原理图" aria-pressed="false"><span>原理图（Schematic）</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/schematics" title="理解 Angular 如何使用原理图。" target="_self"><span>原理图概览</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/schematics-authoring" title="理解原理图的结构。" target="_self"><span>制作原理图</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/schematics-for-libraries" title="使用原理图来把你的库集成进 Angular CLI 中。" target="_self"><span>库的原理图</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/cli-builder" title="使用构建器定制 Angular CLI。" target="_self"><span>CLI 构建器</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/web-worker" title="在 Angular CLI 中使用 Web Worker。" target="_self"><span>Web Worker</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 expanded selected ng-star-inserted" title="关于构建、测试和部署的信息" aria-pressed="true"><span>开发工作流</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 expanded selected"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 expanded selected ng-star-inserted" title="理解 AOT 预先编译器。" aria-pressed="true"><span>AOT 预先编译器</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 expanded selected"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 expanded selected ng-star-inserted" style="position:relative" href="guide/aot-compiler" title="学习为何以及如何使用预先编译器。" target="_self"><span>预先编译</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/angular-compiler-options" title="配置 AOT 编译。" target="_self"><span>Angular 编译器选项</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/aot-metadata-errors" title="解决 AOT 编译错误。" target="_self"><span>AOT 元数据错误</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/template-typecheck" title="Angular 中的模板类型检查。" target="_self"><span>模板类型检查</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/build" title="构建应用及为应用启动开发服务器。" target="_self"><span>构建与运行</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/bazel" title="如何配置你的环境，以利用 Bazel 进行构建和测试。" target="_self"><span>使用 Bazel 进行构建</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/testing" title="测试 Angular 应用的技巧与实践。" target="_self"><span>测试</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/deployment" title="了解如何部署 Angular 应用。" target="_self"><span>发布</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-2 collapsed ng-star-inserted" title="与开发环境和工具集成起来" aria-pressed="false"><span>开发工具集成</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-2 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-3 collapsed ng-star-inserted" style="position:relative" href="guide/language-service" title="使用 Angular 语言服务加速开发。" target="_self"><span>语言服务</span></a></div></aio-nav-item></div></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="工作空间与项目的结构，及其配置文件。" aria-pressed="false"><span>配置</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/file-structure" title="Angular 工作区在文件系统中是怎样的。" target="_self"><span>项目文件结构</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/workspace-config" title="&quot;angular.json&quot; 包含供 CLI 命令使用的工作区和项目默认配置。" target="_self"><span>工作区配置</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/npm-packages" title="开发期间和运行期间所需的 npm 包的说明。" target="_self"><span>npm 包</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/typescript-configuration" title="给 Angular 开发者的 TypeScript 配置。" target="_self"><span>TypeScript 配置</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/browser-support" title="浏览器支持与腻子脚本指南。" target="_self"><span>浏览器支持</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="Angular 的版本发布实践、更新与升级。" aria-pressed="false"><span>发布信息</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/updating" title="如何把 Angular 应用和库升级到最新版本。" target="_self"><span>保持最新</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/releases" title="Angular 的版本、发布、支持、弃用策略及实践。" target="_self"><span>发布实践</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/updating-to-version-9" title="支持把你的应用从 8 升级到 9。" target="_self"><span>升级到第 9 版</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/deprecations" title="弃用的 Angular API 和特性汇总。" target="_self"><span>弃用清单</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/ivy" title="关于 Angular Ivy 的编译与渲染管道。" target="_self"><span>Angular Ivy</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="Angular 语法、编码、术语汇总。" aria-pressed="false"><span>快捷手册</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/cheatsheet" title="关于 Angular 常用编码技术的快速指南。" target="_self"><span>速查表</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/styleguide" title="写出 Angular 风格的程序" target="_self"><span>风格指南</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="guide/glossary" title="Angular 中最重要的词汇的简要定义。" target="_self"><span>词汇表</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><button type="button" class="vertical-menu-item heading level-1 collapsed ng-star-inserted" title="Angular CLI 命令参考手册。" aria-pressed="false"><span>CLI 命令</span><mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><div class="heading-children level-1 collapsed"><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli" title="CLI 工具介绍、命令、语法" target="_self"><span>概览</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/usage-analytics-gathering" title="管理员如何从用户那里收集使用情况分析。" target="_self"><span>使用情况分析</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/add" title="ng add." target="_self"><span>ng add</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/analytics" title="ng analytics." target="_self"><span>ng analytics</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/build" title="ng build." target="_self"><span>ng build</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/config" title="ng config." target="_self"><span>ng config</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/deploy" title="ng deploy." target="_self"><span>ng deploy</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/doc" title="ng doc." target="_self"><span>ng doc</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/e2e" title="ng e2e." target="_self"><span>ng e2e</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/generate" title="ng generate." target="_self"><span>ng generate</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/help" title="ng help." target="_self"><span>ng help</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/lint" title="ng lint." target="_self"><span>ng lint</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/new" title="ng new." target="_self"><span>ng new</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/run" title="ng run." target="_self"><span>ng run</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/serve" title="ng serve." target="_self"><span>ng serve</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/test" title="ng test." target="_self"><span>ng test</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/update" title="ng update." target="_self"><span>ng update</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/version" title="ng version." target="_self"><span>ng version</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-2 collapsed ng-star-inserted" style="position:relative" href="cli/xi18n" title="ng xi18n." target="_self"><span>ng xi18n</span></a></div></aio-nav-item></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-1 collapsed ng-star-inserted" style="position:relative" href="api" title="关于 Angular 中类和值的详细信息。" target="_self"><span>API 参考手册</span></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><div class="mat-divider ng-star-inserted" style="margin:4px 20px;border-top:1px solid #d3d3d3"></div></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-1 collapsed ng-star-inserted" style="position:relative" href="https://github.com/ng-docs/ng-docs.github.io/issues" title="github 上的中文互助问答区" target="_blank"><span>互助问答</span><mat-icon role="img" class="mat-icon notranslate material-icons mat-icon-no-color ng-star-inserted" aria-hidden="true">open_in_new</mat-icon></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-1 collapsed ng-star-inserted" style="position:relative" href="https://material.angular.cn" title="Angular Material 组件库的中文文档" target="_blank"><span>官方 Material 组件库</span><mat-icon role="img" class="mat-icon notranslate material-icons mat-icon-no-color ng-star-inserted" aria-hidden="true">open_in_new</mat-icon></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-1 collapsed ng-star-inserted" style="position:relative" href="https://ng.ant.design/" title="Ant Design 的 Angular 实现，服务于企业级后台产品。" target="_blank"><span>ng-zorro 组件库</span><mat-icon role="img" class="mat-icon notranslate material-icons mat-icon-no-color ng-star-inserted" aria-hidden="true">open_in_new</mat-icon></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-1 collapsed ng-star-inserted" style="position:relative" href="https://devui.design/" title="“华为云” 开源的企业级组件库，核心设计思想是：致简、沉浸、灵活" target="_blank"><span>华为 DevUI 组件库</span><mat-icon role="img" class="mat-icon notranslate material-icons mat-icon-no-color ng-star-inserted" aria-hidden="true">open_in_new</mat-icon></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-1 collapsed ng-star-inserted" style="position:relative" href="https://ng.mobile.ant.design/" title="Ant Design Mobile 的 Angular 实现，服务于无线产品。" target="_blank"><span>ng-zorro mobile 组件库</span><mat-icon role="img" class="mat-icon notranslate material-icons mat-icon-no-color ng-star-inserted" aria-hidden="true">open_in_new</mat-icon></a></div></aio-nav-item><aio-nav-item class="ng-star-inserted"><div class="ng-star-inserted"><a class="vertical-menu-item level-1 collapsed ng-star-inserted" style="position:relative" href="https://flutter.cn/" title="Flutter 中文文档站" target="_blank"><span>友站：Flutter 中文</span><mat-icon role="img" class="mat-icon notranslate material-icons mat-icon-no-color ng-star-inserted" aria-hidden="true">open_in_new</mat-icon></a></div></aio-nav-item></aio-nav-menu><div class="doc-version ng-tns-c18-1"><aio-select><div class="form-select-menu"><button class="form-select-button"><span><strong></strong></span><span>stable (v9.0.0)</span></button></div></aio-select></div></div></mat-sidenav><div class="cdk-visually-hidden cdk-focus-trap-anchor" aria-hidden="true"></div><mat-sidenav-content cdkscrollable="" class="mat-drawer-content mat-sidenav-content ng-star-inserted" style="margin-left:261px"><main role="main" class="sidenav-content" id="guide-aot-compiler"><aio-mode-banner></aio-mode-banner><aio-doc-viewer class=""><div style="opacity:1"><div class="github-links"><a href="https://github.com/angular/angular-cn/edit/aio/aio/content/guide/aot-compiler.md?message=docs%3A%20请简述你的修改..." aria-label="提供编辑建议" title="提供编辑建议"><i class="material-icons" aria-hidden="true" role="img">mode_edit</i></a></div><div class="content"><h1 id="ahead-of-time-aot-compilation" translation-result="on">预先（AOT）编译器<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#ahead-of-time-aot-compilation"><i class="material-icons">link</i></a></h1><aio-toc class="embedded" ng-version="9.0.0-rc.11"><div class="toc-inner no-print collapsed ng-star-inserted"><button type="button" title="Expand/collapse contents" aria-label="Expand/collapse contents" class="toc-heading embedded secondary ng-star-inserted" aria-pressed="false">目录<mat-icon role="img" svgicon="keyboard_arrow_right" class="mat-icon notranslate rotating-icon collapsed mat-icon-no-color" aria-hidden="true"><svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z"></path></svg></mat-icon></button><ul class="toc-list embedded"><li class="h2 ng-star-inserted" title="选择编译器"><a href="guide/aot-compiler#choosing-a-compiler">选择编译器</a></li><li class="h2 ng-star-inserted" title="AOT 工作原理"><a href="guide/aot-compiler#how-aot-works">AOT 工作原理</a></li><li class="h3 ng-star-inserted" title="编译的各个阶段"><a href="guide/aot-compiler#compilation-phases">编译的各个阶段</a></li><li class="h3 secondary ng-star-inserted" title="元数据的限制"><a href="guide/aot-compiler#metadata-restrictions">元数据的限制</a></li><li class="h3 secondary ng-star-inserted" title="配置 AOT 编译"><a href="guide/aot-compiler#configuring-aot-compilation">配置 AOT 编译</a></li><li class="h2 secondary ng-star-inserted" title="阶段 1：分析"><a href="guide/aot-compiler#phase-1-code-analysis">阶段 1：分析</a></li><li class="h3 secondary ng-star-inserted" title="表达式语法限制"><a href="guide/aot-compiler#expression-syntax-limitations">表达式语法限制</a></li><li class="h3 secondary ng-star-inserted" title="不要有箭头函数"><a href="guide/aot-compiler#no-arrow-functions">不要有箭头函数</a></li><li class="h3 secondary ng-star-inserted" title="代码折叠"><a href="guide/aot-compiler#code-folding">代码折叠</a></li><li class="h2 secondary ng-star-inserted" title="阶段 2：代码生成"><a href="guide/aot-compiler#phase-2-code-generation">阶段 2：代码生成</a></li><li class="h3 secondary ng-star-inserted" title="公共符号"><a href="guide/aot-compiler#public-symbols">公共符号</a></li><li class="h3 secondary ng-star-inserted" title="支持的类和函数"><a href="guide/aot-compiler#supported-classes-and-functions">支持的类和函数</a></li><li class="h3 secondary ng-star-inserted" title="函数和静态方法调用"><a href="guide/aot-compiler#functions-and-static-method-calls">函数和静态方法调用</a></li><li class="h3 secondary ng-star-inserted" title="元数据重写"><a href="guide/aot-compiler#metadata-rewriting">元数据重写</a></li><li class="h2 secondary ng-star-inserted" title="阶段3：模板类型检查"><a href="guide/aot-compiler#phase-3-template-type-checking">阶段3：模板类型检查</a></li><li class="h3 secondary ng-star-inserted" title="类型窄化"><a href="guide/aot-compiler#type-narrowing">类型窄化</a></li><li class="h3 secondary ng-star-inserted" title="非空类型断言操作符"><a href="guide/aot-compiler#non-null-type-assertion-operator">非空类型断言操作符</a></li></ul><button type="button" title="Expand/collapse contents" aria-label="Expand/collapse contents" class="toc-more-items embedded material-icons collapsed ng-star-inserted" aria-pressed="false"></button></div></aio-toc><h1 translation-origin="off" id="ahead-of-time-aot-compilation">Ahead-of-time (AOT) compilation<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#ahead-of-time-aot-compilation"><i class="material-icons">link</i></a></h1><p translation-result="on">Angular 应用主要由组件及其 HTML 模板组成。由于浏览器无法直接理解 Angular 所提供的组件和模板，因此 Angular 应用程序需要先进行编译才能在浏览器中运行。</p><p translation-origin="off">An Angular application consists mainly of components and their HTML templates. Because the components and templates provided by Angular cannot be understood by the browser directly, Angular applications require a compilation process before they can run in a browser.</p><p translation-result="on">在浏览器下载和运行代码<em>之前</em>的编译阶段，Angular 预先（AOT）编译器会先把你的 Angular HTML 和 TypeScript 代码转换成高效的 JavaScript 代码。 在构建期间编译应用可以让浏览器中的渲染更快速。</p><p translation-origin="off">The Angular <a href="guide/glossary#aot">ahead-of-time (AOT) compiler</a> converts your Angular HTML and TypeScript code into efficient JavaScript code during the build phase <em>before</em> the browser downloads and runs that code. Compiling your application during the build process provides a faster rendering in the browser.</p><p translation-result="on">本指南中解释了如何指定元数据，并使用一些编译器选项以借助 AOT 编译器来更有效的编译应用。</p><p translation-origin="off">This guide explains how to specify metadata and apply available compiler options to compile your applications efficiently using the AOT compiler.</p><div class="alert is-helpful"><p translation-result="on">观看编译器作者 Tobias Bosch 在 AngularConnect 2016 大会里，对<a href="http://v.youku.com/v_show/id_XMTc1NTE4NTkwOA==.html?from=y1.7-1.4" target="_blank">Angular 编译器</a>的演讲。</p><p translation-origin="off"><a href="https://www.youtube.com/watch?v=kW9cJsvcsGo">Watch compiler author Tobias Bosch explain the Angular compiler</a> at AngularConnect 2016.</p></div><a id="why-aot"></a><p translation-result="on">下面是您可能要使用 AOT 的部分原因。</p><p translation-origin="off">Here are some reasons you might want to use AOT.</p><ul><li><p translation-result="on"><em>更快的渲染</em>。 借助AOT，浏览器可以下载应用的预编译版本。浏览器加载的是可执行代码，因此它可以立即呈现应用，而无需等待先编译好应用。</p><p translation-origin="off"><em>Faster rendering</em> With AOT, the browser downloads a pre-compiled version of the application. The browser loads executable code so it can render the application immediately, without waiting to compile the app first.</p></li></ul><ul><li><p translation-result="on"><em>更少的异步请求</em>。 编译器会在应用 JavaScript 中内<em>联</em>外部 HTML 模板和 CSS 样式表，从而消除了对那些源文件的单独 ajax 请求。</p><p translation-origin="off"><em>Fewer asynchronous requests</em> The compiler <em>inlines</em> external HTML templates and CSS style sheets within the application JavaScript, eliminating separate ajax requests for those source files.</p></li></ul><ul><li><p translation-result="on"><em>较小的 Angular 框架下载大小</em>。 如果已编译应用程序，则无需下载 Angular 编译器。编译器大约是 Angular 本身的一半，因此省略编译器会大大减少应用程序的有效载荷。</p><p translation-origin="off"><em>Smaller Angular framework download size</em> There's no need to download the Angular compiler if the app is already compiled. The compiler is roughly half of Angular itself, so omitting it dramatically reduces the application payload.</p></li></ul><ul><li><p translation-result="on"><em>尽早检测模板错误</em>。 AOT 编译器会在构建步骤中检测并报告模板绑定错误，然后用户才能看到它们。</p><p translation-origin="off"><em>Detect template errors earlier</em> The AOT compiler detects and reports template binding errors during the build step before users can see them.</p></li></ul><ul><li><p translation-result="on"><em>更高的安全性</em>。 AOT 在将 HTML 模板和组件提供给客户端之前就将其编译为 JavaScript 文件。没有要读取的模板，没有潜藏风险的客户端 HTML 或 JavaScript eval，受到注入攻击的机会就更少了。</p><p translation-origin="off"><em>Better security</em> AOT compiles HTML templates and components into JavaScript files long before they are served to the client. With no templates to read and no risky client-side HTML or JavaScript evaluation, there are fewer opportunities for injection attacks.</p></li></ul><a id="overview"></a><h2 id="choosing-a-compiler" translation-result="on">选择编译器<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#choosing-a-compiler"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="choosing-a-compiler">Choosing a compiler<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#choosing-a-compiler"><i class="material-icons">link</i></a></h2><p translation-result="on">Angular 提供了两种方式来编译你的应用：</p><p translation-origin="off">Angular offers two ways to compile your application:</p><ul><li><p translation-result="on"><strong><em>即时编译</em> (JIT)</strong>，它会在运行期间在浏览器中编译你的应用。</p><p translation-origin="off"><strong><em>Just-in-Time</em> (JIT)</strong>, which compiles your app in the browser at runtime.</p></li><li><p translation-result="on"><strong>预先（AOT）编译</strong>，它会在构建时编译你的应用。</p><p translation-origin="off"><strong><em>Ahead-of-Time</em> (AOT)</strong>, which compiles your app at build time.</p></li></ul><p translation-result="on">当你运行 <a href="cli/build"><code>ng build</code></a>（仅编译）或 <a href="cli/serve"><code>ng serve</code></a>（编译并启动本地服务器） 这两个 CLI 命令时 JIT 编译是默认选项：</p><p translation-origin="off">JIT compilation is the default when you run the <a href="cli/build"><code>ng build</code></a>(build only) or <a href="cli/serve"><code>ng serve</code></a>(build and serve locally) CLI commands:</p><code-example language="sh" class="code-shell" ng-version="9.0.0-rc.11"><div style="display:none">ng build ng serve</div><aio-code><pre class="lang-sh prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">ng build
ng serve</span></code>
    </pre></aio-code></code-example><a id="compile"></a><p translation-result="on">要进行 AOT 编译，只要让 <code>ng build</code> 或 <code>ng serve</code> 命令中包含 <code>--aot</code> 标志就行了：</p><p translation-origin="off">For AOT compilation, include the <code>--aot</code> option with the <code>ng build</code> or <code>ng serve</code> command:</p><code-example language="sh" class="code-shell" ng-version="9.0.0-rc.11"><div style="display:none">ng build --aot ng serve --aot</div><aio-code><pre class="lang-sh prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="pln">ng build </span><span class="pun">--</span><span class="pln">aot
ng serve </span><span class="pun">--</span><span class="pln">aot</span></code>
    </pre></aio-code></code-example><div class="alert is-helpful"><p translation-result="on">带有 <code>--prod</code> 标志的 <code>ng build</code> 命令 (<code>ng build --prod</code>) 会默认使用 AOT 编译。</p><p translation-origin="off">The <code>ng build</code> command with the <code>--prod</code> meta-flag (<code>ng build --prod</code>) compiles with AOT by default.</p><p translation-result="on">要了解更多，请参见<a href="cli">CLI 文档</a>，和 <a href="guide/build">构建与运行 Angular 应用</a>。</p><p translation-origin="off">See the <a href="cli">CLI command reference</a> and <a href="guide/build">Building and serving Angular apps</a> for more information.</p></div><h2 id="how-aot-works" translation-result="on">AOT 工作原理<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#how-aot-works"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="how-aot-works">How AOT works<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#how-aot-works"><i class="material-icons">link</i></a></h2><p translation-result="on">Angular AOT 编译器会提取<strong>元数据</strong>来解释应由 Angular 管理的应用程序部分。您可以在<strong>装饰器</strong>（例如 <code>@<a href="api/core/Component" class="code-anchor">Component</a>()</code> 和 <code>@<a href="api/core/Input" class="code-anchor">Input</a>()</code>）中显式指定元数据，也可以在<strong>被装饰的类</strong>的构造函数声明中隐式指定元数据。元数据告诉 Angular 要如何构造应用程序类的实例并在运行时与它们进行交互。</p><p translation-origin="off">The Angular AOT compiler extracts <strong>metadata</strong> to interpret the parts of the application that Angular is supposed to manage. You can specify the metadata explicitly in <strong>decorators</strong> such as <code>@<a href="api/core/Component" class="code-anchor">Component</a>()</code> and <code>@<a href="api/core/Input" class="code-anchor">Input</a>()</code>, or implicitly in the constructor declarations of the decorated classes. The metadata tells Angular how to construct instances of your application classes and interact with them at runtime.</p><p translation-result="on">在下列范例中，<code>@<a href="api/core/Component" class="code-anchor">Component</a>()</code> 元数据对象和类的构造函数会告诉 Angular 如何创建和显示 <code>TypicalComponent</code> 的实例。</p><p translation-origin="off">In the following example, the <code>@<a href="api/core/Component" class="code-anchor">Component</a>()</code> metadata object and the class constructor tell Angular how to create and display an instance of <code>TypicalComponent</code>.</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">@<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-typical', template: '&lt;div&gt;A typical component for {{data.name}}&lt;/div&gt;' )} export class TypicalComponent { @<a href="api/core/Input" class="code-anchor">Input</a>() data: TypicalData; constructor(private someService: SomeService) { ... } }</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
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      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'app-typical'</span><span class="pun">,</span><span class="pln">
  template</span><span class="pun">:</span><span class="pln"> </span><span class="str">'&lt;div&gt;A typical component for {{data.name}}&lt;/div&gt;'</span><span class="pln">
</span><span class="pun">)}</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">TypicalComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="lit">@</span><a href="api/core/Input" class="code-anchor"><span class="lit">Input</span></a><span class="pun">()</span><span class="pln"> data</span><span class="pun">:</span><span class="pln"> </span><span class="typ">TypicalData</span><span class="pun">;</span><span class="pln">
  </span><span class="kwd">constructor</span><span class="pun">(</span><span class="kwd">private</span><span class="pln"> someService</span><span class="pun">:</span><span class="pln"> </span><span class="typ">SomeService</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="pun">...</span><span class="pln"> </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">Angular 编译器只提取<strong>一次</strong>元数据，并且为 <code>TypicalComponent</code> 生成一个<strong>工厂</strong>。 当它需要创建 <code>TypicalComponent</code> 的实例时，Angular 调用这个工厂，工厂会生成一个新的可视元素，并且把它（及其依赖）绑定到组件类的一个新实例上。</p><p translation-origin="off">The Angular compiler extracts the metadata <em>once</em> and generates a <em>factory</em> for <code>TypicalComponent</code>. When it needs to create a <code>TypicalComponent</code> instance, Angular calls the factory, which produces a new visual element, bound to a new instance of the component class with its injected dependency.</p><h3 id="compilation-phases" translation-result="on">编译的各个阶段<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#compilation-phases"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="compilation-phases">Compilation phases<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#compilation-phases"><i class="material-icons">link</i></a></h3><p translation-result="on">AOT 编译分为三个阶段。</p><p translation-origin="off">There are three phases of AOT compilation.</p><ul><li><p translation-result="on">阶段 1 是<em>代码分析</em> 。 在此阶段，TypeScript 编译器和 <em>AOT 收集器</em>会创建源码的表现层。收集器不会尝试解释其收集到的元数据。它只是尽可能地表达元数据，并在检测到元数据语法冲突时记录错误。</p><p translation-origin="off">Phase 1 is <em>code analysis</em>. In this phase, the TypeScript compiler and <em>AOT collector</em> create a representation of the source. The collector does not attempt to interpret the metadata it collects. It represents the metadata as best it can and records errors when it detects a metadata syntax violation.</p></li></ul><ul><li><p translation-result="on">第二阶段是<em>代码生成</em>。 在此阶段，编译器的 <code>StaticReflector</code> 会解释在阶段 1 中收集的元数据，对元数据执行附加验证，如果检测到元数据违反了限制，则抛出错误。</p><p translation-origin="off">Phase 2 is <em>code generation</em>. In this phase, the compiler's <code>StaticReflector</code> interprets the metadata collected in phase 1, performs additional validation of the metadata, and throws an error if it detects a metadata restriction violation.</p></li></ul><ul><li><p translation-result="on">阶段 3 是<em>模板类型检查</em>。在此可选阶段，Angular <em>模板编译器</em>使用 TypeScript 编译器来验证模板中的绑定表达式。您可以通过设置 <code>fullTemplateTypeCheck</code> 配置选项来明确启用此阶段。请参阅 <a href="guide/angular-compiler-options">Angular 编译器选项</a> 。</p><p translation-origin="off">Phase 3 is <em>template type checking</em>. In this optional phase, the Angular <em>template compiler</em> uses the TypeScript compiler to validate the binding expressions in templates. You can enable this phase explicitly by setting the <code>fullTemplateTypeCheck</code> configuration option; see <a href="guide/angular-compiler-options">Angular compiler options</a>.</p></li></ul><h3 id="metadata-restrictions" translation-result="on">元数据的限制<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#metadata-restrictions"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="metadata-restrictions">Metadata restrictions<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#metadata-restrictions"><i class="material-icons">link</i></a></h3><p translation-result="on">你只能使用 TypeScript 的一个<strong>子集</strong>书写元数据，它必须满足下列限制：</p><p translation-origin="off">You write metadata in a <em>subset</em> of TypeScript that must conform to the following general constraints:</p><ul><li><p translation-result="on"><a href="guide/aot-compiler#expression-syntax">表达式语法</a>只支持 JavaScript 的一个有限的子集。</p><p translation-origin="off">Limit <a href="guide/aot-compiler#expression-syntax">expression syntax</a> to the supported subset of JavaScript.</p></li><li><p translation-result="on">只能引用<a href="guide/aot-compiler#code-folding">代码收缩</a>后导出的符号。</p><p translation-origin="off">Only reference exported symbols after <a href="guide/aot-compiler#code-folding">code folding</a>.</p></li><li><p translation-result="on">只能调用编译器<a href="guide/aot-compiler#supported-functions">支持的那些函数</a>。</p><p translation-origin="off">Only call <a href="guide/aot-compiler#supported-functions">functions supported</a> by the compiler.</p></li><li><p translation-result="on">被装饰和用于数据绑定的类成员必须是公共（public）的。</p><p translation-origin="off">Decorated and data-bound class members must be public.</p></li></ul><p translation-result="on">有关准备 AOT 编译应用程序的其他准则和说明，请参阅 <a href="https://medium.com/sparkles-blog/angular-writing-aot-friendly-applications-7b64c8afbe3f">Angular：编写 AOT 友好的应用程序</a> 。</p><p translation-origin="off">For additional guidelines and instructions on preparing an application for AOT compilation, see <a href="https://medium.com/sparkles-blog/angular-writing-aot-friendly-applications-7b64c8afbe3f">Angular: Writing AOT-friendly applications</a>.</p><div class="alert is-helpful"><p translation-result="on">AOT 编译中的错误通常是由于元数据不符合编译器的要求而发生的（下面将更全面地介绍）。为了帮助您理解和解决这些问题，请参阅 <a href="guide/aot-metadata-errors">AOT 元数据错误</a> 。</p><p translation-origin="off">Errors in AOT compilation commonly occur because of metadata that does not conform to the compiler's requirements (as described more fully below). For help in understanding and resolving these problems, see <a href="guide/aot-metadata-errors">AOT Metadata Errors</a>.</p></div><h3 id="configuring-aot-compilation" translation-result="on">配置 AOT 编译<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#configuring-aot-compilation"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="configuring-aot-compilation">Configuring AOT compilation<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#configuring-aot-compilation"><i class="material-icons">link</i></a></h3><p translation-result="on">您可以在 <code>tsconfig.json</code> <a href="guide/typescript-configuration">TypeScript 配置文件</a>中提供控制编译过程的选项。有关可用选项的完整列表，请参见 <a href="guide/angular-compiler-options">Angular 编译器</a>选项。</p><p translation-origin="off">You can provide options in the <code>tsconfig.json</code> <a href="guide/typescript-configuration">TypeScript configuration file</a> that control the compilation process. See <a href="guide/angular-compiler-options">Angular compiler options</a> for a complete list of available options.</p><h2 id="phase-1-code-analysis" translation-result="on">阶段 1：分析<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#phase-1-code-analysis"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="phase-1-code-analysis">Phase 1: Code analysis<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#phase-1-code-analysis"><i class="material-icons">link</i></a></h2><p translation-result="on">TypeScript 编译器会做一些初步的分析工作，它会生成<strong>类型定义文件</strong><code>.d.ts</code>，其中带有类型信息，Angular 编译器需要借助它们来生成代码。</p><p translation-origin="off">The TypeScript compiler does some of the analytic work of the first phase. It emits the <code>.d.ts</code> <em>type definition files</em> with type information that the AOT compiler needs to generate application code.</p><p translation-result="on">同时，AOT <strong>收集器（collector）</strong> 会记录 Angular 装饰器中的元数据，并把它们输出到<strong><code>.metadata.json</code></strong>文件中，和每个 <code>.d.ts</code> 文件相对应。</p><p translation-origin="off">At the same time, the AOT <strong>collector</strong> analyzes the metadata recorded in the Angular decorators and outputs metadata information in <strong><code>.metadata.json</code></strong>files, one per <code>.d.ts</code> file.</p><p translation-result="on">你可以把 <code>.metadata.json</code> 文件看做一个包括全部装饰器的元数据的全景图，就像<a href="https://en.wikipedia.org/wiki/Abstract_syntax_tree">抽象语法树 (AST) </a>一样。</p><p translation-origin="off">You can think of <code>.metadata.json</code> as a diagram of the overall structure of a decorator's metadata, represented as an <a href="https://en.wikipedia.org/wiki/Abstract_syntax_tree">abstract syntax tree (AST)</a>.</p><div class="alert is-helpful"><p translation-result="on">Angular 的 <a href="https://github.com/angular/angular/blob/master/packages/compiler-cli/src/metadata/schema.ts">schema.ts</a> 把这个 JSON 格式表示成了一组 TypeScript 接口。</p><p translation-origin="off">Angular's <a href="https://github.com/angular/angular/blob/master/packages/compiler-cli/src/metadata/schema.ts">schema.ts</a> describes the JSON format as a collection of TypeScript interfaces.</p></div><a id="expression-syntax"></a><h3 id="expression-syntax-limitations" translation-result="on">表达式语法限制<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#expression-syntax-limitations"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="expression-syntax-limitations">Expression syntax limitations<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#expression-syntax-limitations"><i class="material-icons">link</i></a></h3><p translation-result="on">AOT 收集器只能理解 JavaScript 的一个子集。 定义元数据对象时要遵循下列语法限制：</p><p translation-origin="off">The AOT collector only understands a subset of JavaScript. Define metadata objects with the following limited syntax:</p><style>td,th{vertical-align:top}</style><table><tbody><tr><th><p translation-result="on">语法</p><p translation-origin="off">Syntax</p></th><th><p translation-result="on">范例</p><p translation-origin="off">Example</p></th></tr><tr><td><p translation-result="on">对象字面量</p><p translation-origin="off">Literal object</p></td><td><p> <code>{cherry: true, apple: true, mincemeat: false}</code></p></td></tr><tr><td><p translation-result="on">数组字面量</p><p translation-origin="off">Literal array</p></td><td><p> <code>['cherries', 'flour', 'sugar']</code></p></td></tr><tr><td><p translation-result="on">展开数组字面量</p><p translation-origin="off">Spread in literal array</p></td><td><p> <code>['apples', 'flour', ...the_rest]</code></p></td></tr><tr><td><p translation-result="on">函数调用</p><p translation-origin="off">Calls</p></td><td><p> <code>bake(ingredients)</code></p></td></tr><tr><td><p translation-result="on">新建对象</p><p translation-origin="off">New</p></td><td><p> <code>new Oven()</code></p></td></tr><tr><td><p translation-result="on">属性访问</p><p translation-origin="off">Property access</p></td><td><p> <code>pie.slice</code></p></td></tr><tr><td><p translation-result="on">数组索引访问</p><p translation-origin="off">Array index</p></td><td><p> <code>ingredients[0]</code></p></td></tr><tr><td><p translation-result="on">引用标识符</p><p translation-origin="off">Identity reference</p></td><td><p> <code><a href="api/core/Component" class="code-anchor">Component</a></code></p></td></tr><tr><td><p translation-result="on">模板字符串</p><p translation-origin="off">A template string</p></td><td><p> <code><code>pie is ${multiplier} times better than cake</code></p></td></tr><tr><td><p translation-result="on">字符串字面量</p><p translation-origin="off">Literal string</p></td><td><p> <code>pi</code></p></td></tr><tr><td><p translation-result="on">数字字面量</p><p translation-origin="off">Literal number</p></td><td><p> <code>3.14153265</code></p></td></tr><tr><td><p translation-result="on">逻辑字面量</p><p translation-origin="off">Literal boolean</p></td><td><p> <code>true</code></p></td></tr><tr><td><p translation-result="on">null 字面量</p><p translation-origin="off">Literal null</p></td><td><p> <code>null</code></p></td></tr><tr><td><p translation-result="on">受支持的前缀运算符</p><p translation-origin="off">Supported prefix operator</p></td><td><p> <code>!cake</code></p></td></tr><tr><td><p translation-result="on">受支持的二元运算符</p><p translation-origin="off">Supported binary operator</p></td><td><p> <code>a+b</code></p></td></tr><tr><td><p translation-result="on">条件运算符</p><p translation-origin="off">Conditional operator</p></td><td><p> <code>a ? b : c</code></p></td></tr><tr><td><p translation-result="on">括号</p><p translation-origin="off">Parentheses</p></td><td><p> <code>(a+b)</code></p></td></tr></tbody></table><p translation-result="on">如果表达式使用了不支持的语法，收集器就会往 <code>.metadata.json</code> 文件中写入一个错误节点。稍后，如果编译器用到元数据中的这部分内容来生成应用代码，它就会报告这个错误。</p><p translation-origin="off">If an expression uses unsupported syntax, the collector writes an error node to the <code>.metadata.json</code> file. The compiler later reports the error if it needs that piece of metadata to generate the application code.</p><div class="alert is-helpful"><p translation-result="on">如果你希望 <code>ngc</code> 立即汇报这些语法错误，而不要生成带有错误信息的 <code>.metadata.json</code> 文件，可以到 TypeScript 的配置文件 <code>tsconfig.json</code> 中设置 <code>strictMetadataEmit</code> 选项。</p><p translation-origin="off">If you want <code>ngc</code> to report syntax errors immediately rather than produce a <code>.metadata.json</code> file with errors, set the <code>strictMetadataEmit</code> option in the TypeScript configuration file, <code>tsconfig.json</code>.</p><code-example ng-version="9.0.0-rc.11"><div style="display:none">"angularCompilerOptions": { ... "strictMetadataEmit" : true }</div><aio-code><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="str">"angularCompilerOptions"</span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="pun">...</span><span class="pln">
  </span><span class="str">"strictMetadataEmit"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="kwd">true</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">Angular 库通过这个选项来确保所有的 Angular <code>.metadata.json</code> 文件都是干净的。当你要构建自己的代码库时，这也同样是一项最佳实践。</p><p translation-origin="off">Angular libraries have this option to ensure that all Angular <code>.metadata.json</code> files are clean and it is a best practice to do the same when building your own libraries.</p></div><a id="function-expression"></a> <a id="arrow-functions"></a><h3 id="no-arrow-functions" translation-result="on">不要有箭头函数<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#no-arrow-functions"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="no-arrow-functions">No arrow functions<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#no-arrow-functions"><i class="material-icons">link</i></a></h3><p translation-result="on">AOT 编译器不支持 <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/function">函数表达式</a> 和 <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions">箭头函数</a>（也叫 <em>Lambda</em> 函数）。</p><p translation-origin="off">The AOT compiler does not support <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/function">function expressions</a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions">arrow functions</a>, also called <em>lambda</em> functions.</p><p translation-result="on">考虑如下组件装饰器：</p><p translation-origin="off">Consider the following component decorator:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">@<a href="api/core/Component" class="code-anchor">Component</a>({ ... providers: [{provide: server, <a href="api/core/FactorySansProvider#useFactory" class="code-anchor">useFactory</a>: () =&gt; new Server()}] })</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  </span><span class="pun">...</span><span class="pln">
  providers</span><span class="pun">:</span><span class="pln"> </span><span class="pun">[{</span><span class="pln">provide</span><span class="pun">:</span><span class="pln"> server</span><span class="pun">,</span><span class="pln"> </span><a href="api/core/FactorySansProvider#useFactory" class="code-anchor"><span class="pln">useFactory</span></a><span class="pun">:</span><span class="pln"> </span><span class="pun">()</span><span class="pln"> </span><span class="pun">=&gt;</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Server</span><span class="pun">()}]</span><span class="pln">
</span><span class="pun">})</span></code>
    </pre></aio-code></code-example><p translation-result="on">AOT 的收集器不支持在元数据表达式中出现箭头函数 <code>() =&gt; new Server()</code>。 它会在该函数中就地生成一个错误节点。 稍后，当编译器解释该节点时，它就会报告一个错误，让你把这个箭头函数转换成一个<em>导出的函数</em>。</p><p translation-origin="off">The AOT collector does not support the arrow function, <code>() =&gt; new Server()</code>, in a metadata expression. It generates an error node in place of the function. When the compiler later interprets this node, it reports an error that invites you to turn the arrow function into an <em>exported function</em>.</p><p translation-result="on">你可以把它改写成这样来修复这个错误：</p><p translation-origin="off">You can fix the error by converting to this:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">export function serverFactory() { return new Server(); } @<a href="api/core/Component" class="code-anchor">Component</a>({ ... providers: [{provide: server, <a href="api/core/FactorySansProvider#useFactory" class="code-anchor">useFactory</a>: serverFactory}] })</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">export</span><span class="pln"> </span><span class="kwd">function</span><span class="pln"> serverFactory</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="kwd">return</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Server</span><span class="pun">();</span><span class="pln">
</span><span class="pun">}</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  </span><span class="pun">...</span><span class="pln">
  providers</span><span class="pun">:</span><span class="pln"> </span><span class="pun">[{</span><span class="pln">provide</span><span class="pun">:</span><span class="pln"> server</span><span class="pun">,</span><span class="pln"> </span><a href="api/core/FactorySansProvider#useFactory" class="code-anchor"><span class="pln">useFactory</span></a><span class="pun">:</span><span class="pln"> serverFactory</span><span class="pun">}]</span><span class="pln">
</span><span class="pun">})</span></code>
    </pre></aio-code></code-example><p translation-result="on">在版本 5 和更高版本中，编译器会在发出 <code>.js</code> 文件时自动执行此重写。</p><p translation-origin="off">In version 5 and later, the compiler automatically performs this rewriting while emitting the <code>.js</code> file.</p><a id="exported-symbols"></a> <a id="code-folding"></a><h3 id="code-folding" translation-result="on">代码折叠<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#code-folding"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="code-folding">Code folding<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#code-folding"><i class="material-icons">link</i></a></h3><p translation-result="on">编译器只会解析到<strong><em>已导出</em></strong>符号的引用。 收集器可以在收集期间执行表达式，并用其结果记录到 <code>.metadata.json</code> 中（而不是原始表达式中）。 这样可以让你把非导出符号的使用限制在表达式中。</p><p translation-origin="off">The compiler can only resolve references to <strong><em>exported</em></strong> symbols. The collector, however, can evaluate an expression during collection and record the result in the <code>.metadata.json</code>, rather than the original expression. This allows you to make limited use of non-exported symbols within expressions.</p><p translation-result="on">比如，收集器可以执行表达式 <code>1 + 2 + 3 + 4</code>，并使用它的结果 <code>10</code> 替换它。</p><p translation-origin="off">For example, the collector can evaluate the expression <code>1 + 2 + 3 + 4</code> and replace it with the result, <code>10</code>.</p><p translation-result="on">这个过程被称为<em>折叠</em>。能用这种方式进行简化的表达式就是<em>可折叠的</em>。</p><p translation-origin="off">This process is called <em>folding</em>. An expression that can be reduced in this manner is <em>foldable</em>.</p><a id="var-declaration"></a><p translation-result="on">收集器可以计算对模块局部变量的 <code>const</code> 声明和初始化过的 <code>var</code> 和 <code>let</code> 声明，并从 <code>.metadata.json</code> 文件中移除它们。</p><p translation-origin="off">The collector can evaluate references to module-local <code>const</code> declarations and initialized <code>var</code> and <code>let</code> declarations, effectively removing them from the <code>.metadata.json</code> file.</p><p translation-result="on">考虑下列组件定义：</p><p translation-origin="off">Consider the following component definition:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">const template = '&lt;div&gt;{{hero.name}}&lt;/div&gt;'; @<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-hero', template: template }) export class HeroComponent { @<a href="api/core/Input" class="code-anchor">Input</a>() hero: Hero; }</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">const</span><span class="pln"> template </span><span class="pun">=</span><span class="pln"> </span><span class="str">'&lt;div&gt;{{hero.name}}&lt;/div&gt;'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'app-hero'</span><span class="pun">,</span><span class="pln">
  template</span><span class="pun">:</span><span class="pln"> template
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">HeroComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="lit">@</span><a href="api/core/Input" class="code-anchor"><span class="lit">Input</span></a><span class="pun">()</span><span class="pln"> hero</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Hero</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">编译器不能引用 <code>template</code> 常量，因为它是未导出的。 但是收集器可以通过内联 <code>template</code> 常量的方式把它<em>折叠</em>进元数据定义中。 最终的结果和你以前的写法是一样的：</p><p translation-origin="off">The compiler could not refer to the <code>template</code> constant because it isn't exported. The collector, however, can fold the <code>template</code> constant into the metadata definition by in-lining its contents. The effect is the same as if you had written:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">@<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-hero', template: '&lt;div&gt;{{hero.name}}&lt;/div&gt;' }) export class HeroComponent { @<a href="api/core/Input" class="code-anchor">Input</a>() hero: Hero; }</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'app-hero'</span><span class="pun">,</span><span class="pln">
  template</span><span class="pun">:</span><span class="pln"> </span><span class="str">'&lt;div&gt;{{hero.name}}&lt;/div&gt;'</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">HeroComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="lit">@</span><a href="api/core/Input" class="code-anchor"><span class="lit">Input</span></a><span class="pun">()</span><span class="pln"> hero</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Hero</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">这里没有对 <code>template</code> 的引用，因此，当编译器稍后对位于 <code>.metadata.json</code> 中的收集器输出进行解释时，不会再出问题。</p><p translation-origin="off">There is no longer a reference to <code>template</code> and, therefore, nothing to trouble the compiler when it later interprets the <em>collector's</em> output in <code>.metadata.json</code>.</p><p translation-result="on">你还可以通过把 <code>template</code> 常量包含在其它表达式中来让这个例子深入一点：</p><p translation-origin="off">You can take this example a step further by including the <code>template</code> constant in another expression:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">const template = '&lt;div&gt;{{hero.name}}&lt;/div&gt;'; @<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-hero', template: template + '&lt;div&gt;{{hero.title}}&lt;/div&gt;' }) export class HeroComponent { @<a href="api/core/Input" class="code-anchor">Input</a>() hero: Hero; }</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">const</span><span class="pln"> template </span><span class="pun">=</span><span class="pln"> </span><span class="str">'&lt;div&gt;{{hero.name}}&lt;/div&gt;'</span><span class="pun">;</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'app-hero'</span><span class="pun">,</span><span class="pln">
  template</span><span class="pun">:</span><span class="pln"> template </span><span class="pun">+</span><span class="pln"> </span><span class="str">'&lt;div&gt;{{hero.title}}&lt;/div&gt;'</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">HeroComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="lit">@</span><a href="api/core/Input" class="code-anchor"><span class="lit">Input</span></a><span class="pun">()</span><span class="pln"> hero</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Hero</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">收集器把该表达式缩减成其等价的<em>已折叠</em>字符串：</p><p translation-origin="off">The collector reduces this expression to its equivalent <em>folded</em> string:</p><code-example ng-version="9.0.0-rc.11"><div style="display:none">'&lt;div&gt;{{hero.name}}&lt;/div&gt;&lt;div&gt;{{hero.title}}&lt;/div&gt;'</div><aio-code><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="str">'&lt;div&gt;{{hero.name}}&lt;/div&gt;&lt;div&gt;{{hero.title}}&lt;/div&gt;'</span></code>
    </pre></aio-code></code-example><h4 id="foldable-syntax" translation-result="on">可折叠的语法<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#foldable-syntax"><i class="material-icons">link</i></a></h4><h4 translation-origin="off" id="foldable-syntax">Foldable syntax<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#foldable-syntax"><i class="material-icons">link</i></a></h4><p translation-result="on">下表中描述了收集器可以折叠以及不能折叠哪些表达式：</p><p translation-origin="off">The following table describes which expressions the collector can and cannot fold:</p><style>td,th{vertical-align:top}</style><table><tbody><tr><th><p translation-result="on">语法</p><p translation-origin="off">Syntax</p></th><th><p translation-result="on">可折叠？</p><p translation-origin="off">Foldable</p></th></tr><tr><td><p translation-result="on">对象字面量</p><p translation-origin="off">Literal object</p></td><td><p translation-result="on">是</p><p translation-origin="off">Yes</p></td></tr><tr><td><p translation-result="on">数组字面量</p><p translation-origin="off">Literal array</p></td><td><p translation-result="on">是</p><p translation-origin="off">Yes</p></td></tr><tr><td><p translation-result="on">展开数组字面量</p><p translation-origin="off">Spread in literal array</p></td><td><p translation-result="on">否</p><p translation-origin="off">no</p></td></tr><tr><td><p translation-result="on">函数调用</p><p translation-origin="off">Calls</p></td><td><p translation-result="on">否</p><p translation-origin="off">no</p></td></tr><tr><td><p translation-result="on">新建对象</p><p translation-origin="off">New</p></td><td><p translation-result="on">否</p><p translation-origin="off">no</p></td></tr><tr><td><p translation-result="on">属性访问</p><p translation-origin="off">Property access</p></td><td><p translation-result="on">如果目标对象也是可折叠的，则是</p><p translation-origin="off">yes, if target is foldable</p></td></tr><tr><td><p translation-result="on">数组索引访问</p><p translation-origin="off">Array index</p></td><td><p translation-result="on">如果目标数组和索引都是可折叠的，则是</p><p translation-origin="off">yes, if target and index are foldable</p></td></tr><tr><td><p translation-result="on">引用标识符</p><p translation-origin="off">Identity reference</p></td><td><p translation-result="on">如果引用的是局部标识符，则是</p><p translation-origin="off">yes, if it is a reference to a local</p></td></tr><tr><td><p translation-result="on">没有替换表达式的模板字符串</p><p translation-origin="off">A template with no substitutions</p></td><td><p translation-result="on">是</p><p translation-origin="off">yes</p></td></tr><tr><td><p translation-result="on">有替换表达式的模板字符串</p><p translation-origin="off">A template with substitutions</p></td><td><p translation-result="on">如果替换表达式是可折叠的，则是</p><p translation-origin="off">yes, if the substitutions are foldable</p></td></tr><tr><td><p translation-result="on">字符串字面量</p><p translation-origin="off">Literal string</p></td><td><p translation-result="on">是</p><p translation-origin="off">yes</p></td></tr><tr><td><p translation-result="on">数字字面量</p><p translation-origin="off">Literal number</p></td><td><p translation-result="on">是</p><p translation-origin="off">yes</p></td></tr><tr><td><p translation-result="on">逻辑字面量</p><p translation-origin="off">Literal boolean</p></td><td><p translation-result="on">是</p><p translation-origin="off">yes</p></td></tr><tr><td><p translation-result="on">null 字面量</p><p translation-origin="off">Literal null</p></td><td><p translation-result="on">是</p><p translation-origin="off">yes</p></td></tr><tr><td><p translation-result="on">受支持的前缀运算符</p><p translation-origin="off">Supported prefix operator</p></td><td><p translation-result="on">如果操作数是可折叠的，则是</p><p translation-origin="off">yes, if operand is foldable</p></td></tr><tr><td><p translation-result="on">受支持的二元运算符</p><p translation-origin="off">Supported binary operator</p></td><td><p translation-result="on">如果左操作数和右操作数都是可折叠的，则是</p><p translation-origin="off">yes, if both left and right are foldable</p></td></tr><tr><td><p translation-result="on">条件运算符</p><p translation-origin="off">Conditional operator</p></td><td><p translation-result="on">如果条件是可折叠的，则是</p><p translation-origin="off">yes, if condition is foldable</p></td></tr><tr><td><p translation-result="on">括号</p><p translation-origin="off">Parentheses</p></td><td><p translation-result="on">如果表达式是可折叠的，则是</p><p translation-origin="off">yes, if the expression is foldable</p></td></tr></tbody></table><p translation-result="on">如果表达式是不可折叠的，那么收集器就会把它作为一个 <a href="https://en.wikipedia.org/wiki/Abstract_syntax_tree">AST</a>（抽象语法树） 写入 <code>.metadata.json</code> 中，留给编译器去解析。</p><p translation-origin="off">If an expression is not foldable, the collector writes it to <code>.metadata.json</code> as an <a href="https://en.wikipedia.org/wiki/Abstract_syntax_tree">AST</a> for the compiler to resolve.</p><h2 id="phase-2-code-generation" translation-result="on">阶段 2：代码生成<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#phase-2-code-generation"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="phase-2-code-generation">Phase 2: code generation<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#phase-2-code-generation"><i class="material-icons">link</i></a></h2><p translation-result="on">收集器不会试图理解它收集并输出到 <code>.metadata.json</code> 中的元数据，它所能做的只是尽可能准确的表述这些元数据，并在检测到元数据中的语法违规时记录这些错误。</p><p translation-origin="off">The collector makes no attempt to understand the metadata that it collects and outputs to <code>.metadata.json</code>. It represents the metadata as best it can and records errors when it detects a metadata syntax violation.</p><p translation-result="on">解释这些 <code>.metadata.json</code> 是编译器在代码生成阶段要承担的工作。</p><p translation-origin="off">It's the compiler's job to interpret the <code>.metadata.json</code> in the code generation phase.</p><p translation-result="on">编译器理解收集器支持的所有语法形式，但是它也可能拒绝那些虽然<em>语法正确</em>但<em>语义</em>违反了编译器规则的元数据。</p><p translation-origin="off">The compiler understands all syntax forms that the collector supports, but it may reject <em>syntactically</em> correct metadata if the <em>semantics</em> violate compiler rules.</p><h3 id="public-symbols" translation-result="on">公共符号<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#public-symbols"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="public-symbols">Public symbols<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#public-symbols"><i class="material-icons">link</i></a></h3><p translation-result="on">编译器只能引用<em>已导出的符号</em>。</p><p translation-origin="off">The compiler can only reference <em>exported symbols</em>.</p><ul><li><p translation-result="on">带有装饰器的类成员必须是公开的。你不可能把一个私有或内部使用的属性做成 <code>@<a href="api/core/Input" class="code-anchor">Input</a>()</code>。</p><p translation-origin="off">Decorated component class members must be public. You cannot make an <code>@<a href="api/core/Input" class="code-anchor">Input</a>()</code> property private or protected.</p></li><li><p translation-result="on">数据绑定的属性同样必须是公开的。</p><p translation-origin="off">Data bound properties must also be public.</p></li></ul><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">// BAD CODE - title is private @<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'app-root', template: '&lt;h1&gt;{{title}}&lt;/h1&gt;' }) export class AppComponent { private title = 'My App'; // Bad }</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="com">// BAD CODE - title is private</span><span class="pln">
</span><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'app-root'</span><span class="pun">,</span><span class="pln">
  template</span><span class="pun">:</span><span class="pln"> </span><span class="str">'&lt;h1&gt;{{title}}&lt;/h1&gt;'</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">AppComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="kwd">private</span><span class="pln"> title </span><span class="pun">=</span><span class="pln"> </span><span class="str">'My App'</span><span class="pun">;</span><span class="pln"> </span><span class="com">// Bad</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><a id="supported-functions"></a><h3 id="supported-classes-and-functions" translation-result="on">支持的类和函数<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#supported-classes-and-functions"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="supported-classes-and-functions">Supported classes and functions<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#supported-classes-and-functions"><i class="material-icons">link</i></a></h3><p translation-result="on">只要语法有效，收集器就可以用 <code>new</code> 来表示函数调用或对象创建。但是，编译器在后面可以拒绝生成对<em>特定</em>函数的调用或对<em>特定</em>对象的创建。</p><p translation-origin="off">The collector can represent a function call or object creation with <code>new</code> as long as the syntax is valid. The compiler, however, can later refuse to generate a call to a <em>particular</em> function or creation of a <em>particular</em> object.</p><p translation-result="on">编译器只能创建某些类的实例，仅支持核心装饰器，并且仅支持对返回表达式的宏（函数或静态方法）的调用。</p><p translation-origin="off">The compiler can only create instances of certain classes, supports only core decorators, and only supports calls to macros (functions or static methods) that return expressions.</p><ul><li><p translation-result="on">新建实例</p><p translation-origin="off">New instances</p><p translation-result="on">编译器只允许创建来自 <code>@angular/core</code> 的 <code><a href="api/core/InjectionToken" class="code-anchor">InjectionToken</a></code> 类创建实例。</p><p translation-origin="off">The compiler only allows metadata that create instances of the class <code><a href="api/core/InjectionToken" class="code-anchor">InjectionToken</a></code> from <code>@angular/core</code>.</p></li><li><p translation-result="on">支持的装饰器</p><p translation-origin="off">Supported decorators</p><p translation-result="on">编译器只支持来自 <a href="api/core#decorators"><code>@angular/core</code> 模块</a>的 Angular 装饰器的元数据。</p><p translation-origin="off">The compiler only supports metadata for the <a href="api/core#decorators">Angular decorators in the <code>@angular/core</code> module</a>.</p></li><li><p translation-result="on">函数调用</p><p translation-origin="off">Function calls</p><p translation-result="on">工厂函数必须导出为命名函数。 AOT 编译器不支持用 Lambda 表达式（箭头函数）充当工厂函数。</p><p translation-origin="off">Factory functions must be exported, named functions. The AOT compiler does not support lambda expressions ("arrow functions") for factory functions.</p></li></ul><a id="function-calls"></a><h3 id="functions-and-static-method-calls" translation-result="on">函数和静态方法调用<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#functions-and-static-method-calls"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="functions-and-static-method-calls">Functions and static method calls<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#functions-and-static-method-calls"><i class="material-icons">link</i></a></h3><p translation-result="on">收集器接受任何只包含一个 <code>return</code> 语句的函数或静态方法。 编译器也支持在返回表达式的函数或静态函数中使用<em>宏</em>。</p><p translation-origin="off">The collector accepts any function or static method that contains a single <code>return</code> statement. The compiler, however, only supports macros in the form of functions or static methods that return an <em>expression</em>.</p><p translation-result="on">考虑下面的函数：</p><p translation-origin="off">For example, consider the following function:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">export function wrapInArray&lt;T&gt;(value: T): T[] { return [value]; }</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">export</span><span class="pln"> </span><span class="kwd">function</span><span class="pln"> wrapInArray</span><span class="pun">&lt;</span><span class="pln">T</span><span class="pun">&gt;(</span><span class="pln">value</span><span class="pun">:</span><span class="pln"> T</span><span class="pun">):</span><span class="pln"> T</span><span class="pun">[]</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  </span><span class="kwd">return</span><span class="pln"> </span><span class="pun">[</span><span class="pln">value</span><span class="pun">];</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">你可以在元数据定义中调用 <code>wrapInArray</code>，因为它所返回的表达式的值满足编译器支持的 JavaScript 受限子集。</p><p translation-origin="off">You can call the <code>wrapInArray</code> in a metadata definition because it returns the value of an expression that conforms to the compiler's restrictive JavaScript subset.</p><p translation-result="on">你还可以这样使用 <code>wrapInArray()</code>：</p><p translation-origin="off">You might use <code>wrapInArray()</code> like this:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">@<a href="api/core/NgModule" class="code-anchor">NgModule</a>({ declarations: wrapInArray(TypicalComponent) }) export class TypicalModule {}</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/NgModule" class="code-anchor"><span class="lit">NgModule</span></a><span class="pun">({</span><span class="pln">
  declarations</span><span class="pun">:</span><span class="pln"> wrapInArray</span><span class="pun">(</span><span class="typ">TypicalComponent</span><span class="pun">)</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">TypicalModule</span><span class="pln"> </span><span class="pun">{}</span></code>
    </pre></aio-code></code-example><p translation-result="on">编译器会把这种用法处理成你以前的写法：</p><p translation-origin="off">The compiler treats this usage as if you had written:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">@<a href="api/core/NgModule" class="code-anchor">NgModule</a>({ declarations: [TypicalComponent] }) export class TypicalModule {}</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/NgModule" class="code-anchor"><span class="lit">NgModule</span></a><span class="pun">({</span><span class="pln">
  declarations</span><span class="pun">:</span><span class="pln"> </span><span class="pun">[</span><span class="typ">TypicalComponent</span><span class="pun">]</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">TypicalModule</span><span class="pln"> </span><span class="pun">{}</span></code>
    </pre></aio-code></code-example><p translation-result="on">Angular 的 <a href="api/router/RouterModule"><code>RouterModule</code></a>导出了两个静态宏函数 <code>forRoot</code> 和 <code>forChild</code>，以帮助声明根路由和子路由。 查看这些方法的<a href="https://github.com/angular/angular/blob/master/packages/router/src/router_module.ts#L139" title="RouterModule.forRoot source code">源码</a>，以了解宏函数是如何简化复杂的 <a href="guide/ngmodules">NgModule</a> 配置的。</p><p translation-origin="off">The Angular <a href="api/router/RouterModule"><code>RouterModule</code></a>exports two macro static methods, <code>forRoot</code> and <code>forChild</code>, to help declare root and child routes. Review the <a href="https://github.com/angular/angular/blob/master/packages/router/src/router_module.ts#L139" title="RouterModule.forRoot source code">source code</a> for these methods to see how macros can simplify configuration of complex <a href="guide/ngmodules">NgModules</a>.</p><a id="metadata-rewriting"></a><h3 id="metadata-rewriting" translation-result="on">元数据重写<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#metadata-rewriting"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="metadata-rewriting">Metadata rewriting<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#metadata-rewriting"><i class="material-icons">link</i></a></h3><p translation-result="on">编译器会对含有 <code>useClass</code>、<code><a href="api/core/ValueSansProvider#useValue" class="code-anchor">useValue</a></code>、<code><a href="api/core/FactorySansProvider#useFactory" class="code-anchor">useFactory</a></code> 和 <code>data</code> 的对象字面量进行特殊处理，把用这些字段之一初始化的表达式转换成一个导出的变量，并用它替换该表达式。 这个重写表达式的过程，会消除它们受到的所有限制，因为编译器并不需要知道该表达式的值，它只要能生成对该值的引用就行了。</p><p translation-origin="off">The compiler treats object literals containing the fields <code>useClass</code>, <code><a href="api/core/ValueSansProvider#useValue" class="code-anchor">useValue</a></code>, <code><a href="api/core/FactorySansProvider#useFactory" class="code-anchor">useFactory</a></code>, and <code>data</code> specially, converting the expression initializing one of these fields into an exported variable that replaces the expression. This process of rewriting these expressions removes all the restrictions on what can be in them because the compiler doesn't need to know the expression's value—it just needs to be able to generate a reference to the value.</p><p translation-result="on">你可以这样写：</p><p translation-origin="off">You might write something like:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">class TypicalServer { } @<a href="api/core/NgModule" class="code-anchor">NgModule</a>({ providers: [{provide: SERVER, <a href="api/core/FactorySansProvider#useFactory" class="code-anchor">useFactory</a>: () =&gt; TypicalServer}] }) export class TypicalModule {}</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">class</span><span class="pln"> </span><span class="typ">TypicalServer</span><span class="pln"> </span><span class="pun">{</span><span class="pln">

</span><span class="pun">}</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/NgModule" class="code-anchor"><span class="lit">NgModule</span></a><span class="pun">({</span><span class="pln">
  providers</span><span class="pun">:</span><span class="pln"> </span><span class="pun">[{</span><span class="pln">provide</span><span class="pun">:</span><span class="pln"> SERVER</span><span class="pun">,</span><span class="pln"> </span><a href="api/core/FactorySansProvider#useFactory" class="code-anchor"><span class="pln">useFactory</span></a><span class="pun">:</span><span class="pln"> </span><span class="pun">()</span><span class="pln"> </span><span class="pun">=&gt;</span><span class="pln"> </span><span class="typ">TypicalServer</span><span class="pun">}]</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">TypicalModule</span><span class="pln"> </span><span class="pun">{}</span></code>
    </pre></aio-code></code-example><p translation-result="on">如果不重写，这就是无效的，因为这里不支持 Lambda 表达式，而且 <code>TypicalServer</code> 也没有被导出。 为了支持这种写法，编译器自动把它重写成了这样：</p><p translation-origin="off">Without rewriting, this would be invalid because lambdas are not supported and <code>TypicalServer</code> is not exported. To allow this, the compiler automatically rewrites this to something like:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">class TypicalServer { } export const ɵ0 = () =&gt; new TypicalServer(); @<a href="api/core/NgModule" class="code-anchor">NgModule</a>({ providers: [{provide: SERVER, <a href="api/core/FactorySansProvider#useFactory" class="code-anchor">useFactory</a>: ɵ0}] }) export class TypicalModule {}</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">class</span><span class="pln"> </span><span class="typ">TypicalServer</span><span class="pln"> </span><span class="pun">{</span><span class="pln">

</span><span class="pun">}</span><span class="pln">

</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">const</span><span class="pln"> </span><span class="pun">ɵ</span><span class="lit">0</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="pun">()</span><span class="pln"> </span><span class="pun">=&gt;</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">TypicalServer</span><span class="pun">();</span><span class="pln">

</span><span class="lit">@</span><a href="api/core/NgModule" class="code-anchor"><span class="lit">NgModule</span></a><span class="pun">({</span><span class="pln">
  providers</span><span class="pun">:</span><span class="pln"> </span><span class="pun">[{</span><span class="pln">provide</span><span class="pun">:</span><span class="pln"> SERVER</span><span class="pun">,</span><span class="pln"> </span><a href="api/core/FactorySansProvider#useFactory" class="code-anchor"><span class="pln">useFactory</span></a><span class="pun">:</span><span class="pln"> </span><span class="pun">ɵ</span><span class="lit">0</span><span class="pun">}]</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">export</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">TypicalModule</span><span class="pln"> </span><span class="pun">{}</span></code>
    </pre></aio-code></code-example><p translation-result="on">这就让编译器能在工厂中生成一个对 <code>ɵ0</code> 的引用，而不用知道 <code>ɵ0</code> 中包含的值到底是什么。</p><p translation-origin="off">This allows the compiler to generate a reference to <code>ɵ0</code> in the factory without having to know what the value of <code>ɵ0</code> contains.</p><p translation-result="on">编译器会在生成 <code>.js</code> 文件期间进行这种重写。它不会重写 <code>.d.ts</code> 文件，所以 TypeScript 也不会把这个变量当做一项导出，因此也就不会污染 ES 模块中导出的 API。</p><p translation-origin="off">The compiler does the rewriting during the emit of the <code>.js</code> file. It does not, however, rewrite the <code>.d.ts</code> file, so TypeScript doesn't recognize it as being an export. and it does not interfere with the ES module's exported API.</p><a id="binding-expression-validation"></a><h2 id="phase-3-template-type-checking" translation-result="on">阶段3：模板类型检查<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#phase-3-template-type-checking"><i class="material-icons">link</i></a></h2><h2 translation-origin="off" id="phase-3-template-type-checking">Phase 3: Template type checking<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#phase-3-template-type-checking"><i class="material-icons">link</i></a></h2><p translation-result="on">Angular 编译器最有用的功能之一就是能够对模板中的表达式进行类型检查，在由于出错而导致运行时崩溃之前就捕获任何错误。在模板类型检查阶段，Angular 模板编译器会使用 TypeScript 编译器来验证模板中的绑定表达式。</p><p translation-origin="off">One of the Angular compiler's most helpful features is the ability to type-check expressions within templates, and catch any errors before they cause crashes at runtime. In the template type-checking phase, the Angular template compiler uses the TypeScript compiler to validate the binding expressions in templates.</p><p translation-result="on">通过在该项目的 <code>tsconfig.json</code> 的 <code>"angularCompilerOptions"</code>中添加编译器选项 <code>"fullTemplateTypeCheck"</code>，可以显式启用本阶段（见<a href="guide/angular-compiler-options"> Angular 编译器选项</a> ）。</p><p translation-origin="off">Enable this phase explicitly by adding the compiler option <code>"fullTemplateTypeCheck"</code> in the <code>"angularCompilerOptions"</code> of the project's <code>tsconfig.json</code> (see <a href="guide/angular-compiler-options">Angular Compiler Options</a>).</p><div class="alert is-helpful"><p translation-result="on">在 <a href="guide/ivy">Angular Ivy 中</a> 中，模板类型检查器已被完全重写，以使其功能更强大，更严格。这意味着它可以捕获以前的类型检查器无法检测到的各种新错误。</p><p translation-origin="off">In <a href="guide/ivy">Angular Ivy</a>, the template type checker has been completely rewritten to be more capable as well as stricter, meaning it can catch a variety of new errors that the previous type checker would not detect.</p><p translation-result="on">这就导致了，以前在 View Engine 下能通过编译的模板可能无法在 Ivy 下通过类型检查。之所以会发生这种情况，是因为 Ivy 更严格的检查会捕获真正的错误：或者因为应用程序代码中的类型不正确，或者因为应用程序使用的库中的类型不正确或不够具体。</p><p translation-origin="off">As a result, templates that previously compiled under View Engine can fail type checking under Ivy. This can happen because Ivy's stricter checking catches genuine errors, or because application code is not typed correctly, or because the application uses libraries in which typings are inaccurate or not specific enough.</p><p translation-result="on">在版本 9 中，默认未启用此更严格的类型检查，但可以通过设置 <code>strictTemplates</code> 配置选项来启用它。我们真的希望将来可以把严格类型检查作为默认值。</p><p translation-origin="off">This stricter type checking is not enabled by default in version 9, but can be enabled by setting the <code>strictTemplates</code> configuration option. We do expect to make strict type checking the default in the future.</p></div><p translation-result="on">当模板绑定表达式中检测到类型错误时，进行模板验证时就会生成错误。这和 TypeScript 编译器在处理 <code>.ts</code> 文件中的代码时报告错误很相似。</p><p translation-origin="off">Template validation produces error messages when a type error is detected in a template binding expression, similar to how type errors are reported by the TypeScript compiler against code in a <code>.ts</code> file.</p><p translation-result="on">比如，考虑下列组件：</p><p translation-origin="off">For example, consider the following component:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">@<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'my-component', template: '{{person.addresss.street}}' }) class MyComponent { person?: Person; }</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'my-component'</span><span class="pun">,</span><span class="pln">
  template</span><span class="pun">:</span><span class="pln"> </span><span class="str">'{{person.addresss.street}}'</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">class</span><span class="pln"> </span><span class="typ">MyComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  person</span><span class="pun">?:</span><span class="pln"> </span><span class="typ">Person</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">这会生成如下错误：</p><p translation-origin="off">This produces the following error:</p><code-example ng-version="9.0.0-rc.11"><div style="display:none">my.component.ts.MyComponent.html(1,1): : Property 'addresss' does not exist on type 'Person'. Did you mean 'address'?</div><aio-code><pre class="lang- prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="kwd">my</span><span class="pun">.</span><span class="pln">component</span><span class="pun">.</span><span class="pln">ts</span><span class="pun">.</span><span class="typ">MyComponent</span><span class="pun">.</span><span class="pln">html</span><span class="pun">(</span><span class="lit">1</span><span class="pun">,</span><span class="lit">1</span><span class="pun">):</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="typ">Property</span><span class="pln"> </span><span class="str">'addresss'</span><span class="pln"> does </span><span class="kwd">not</span><span class="pln"> exist on type </span><span class="str">'Person'</span><span class="pun">.</span><span class="pln"> </span><span class="typ">Did</span><span class="pln"> you mean </span><span class="str">'address'</span><span class="pun">?</span></code>
    </pre></aio-code></code-example><p translation-result="on">错误信息中汇报的文件名 <code>my.component.ts.MyComponent.html</code> 是一个由模板编译器生成出的合成文件， 用于保存 <code>MyComponent</code> 类的模板内容。 编译器永远不会把这个文件写入磁盘。这个例子中，这里的行号和列号都是相对于 <code>MyComponent</code> 的 <code>@<a href="api/core/Component" class="code-anchor">Component</a></code> 注解中的模板字符串的。 如果组件使用 <code><a href="api/core/Component#templateUrl" class="code-anchor">templateUrl</a></code> 来代替 <code>template</code>，这些错误就会在 <code><a href="api/core/Component#templateUrl" class="code-anchor">templateUrl</a></code> 引用的 HTML 文件中汇报，而不是这个合成文件中。</p><p translation-origin="off">The file name reported in the error message, <code>my.component.ts.MyComponent.html</code>, is a synthetic file generated by the template compiler that holds contents of the <code>MyComponent</code> class template. The compiler never writes this file to disk. The line and column numbers are relative to the template string in the <code>@<a href="api/core/Component" class="code-anchor">Component</a></code> annotation of the class, <code>MyComponent</code> in this case. If a component uses <code><a href="api/core/Component#templateUrl" class="code-anchor">templateUrl</a></code> instead of <code>template</code>, the errors are reported in the HTML file referenced by the <code><a href="api/core/Component#templateUrl" class="code-anchor">templateUrl</a></code> instead of a synthetic file.</p><p translation-result="on">错误的位置是从包含出错的插值表达式的那个文本节点开始的。 如果错误是一个属性绑定，比如 <code>[value]="person.address.street"</code> ，错误的位置就是那个包含错误的属性的位置。</p><p translation-origin="off">The error location is the beginning of the text node that contains the interpolation expression with the error. If the error is in an attribute binding such as <code>[value]="person.address.street"</code>, the error location is the location of the attribute that contains the error.</p><p translation-result="on">这个验证过程使用 TypeScript 的类型检查器，这些选项也会提供给 TypeScript 编译器以控制类型验证的详细程度。 比如，如果指定了 <code>strictTypeChecks</code>，就会像上面的错误信息一样报告 <code>my.component.ts.MyComponent.html(1,1): : Object is possibly 'undefined'</code> 错误。</p><p translation-origin="off">The validation uses the TypeScript type checker and the options supplied to the TypeScript compiler to control how detailed the type validation is. For example, if the <code>strictTypeChecks</code> is specified, the error <code>my.component.ts.MyComponent.html(1,1): : Object is possibly 'undefined'</code> is reported as well as the above error message.</p><h3 id="type-narrowing" translation-result="on">类型窄化<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#type-narrowing"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="type-narrowing">Type narrowing<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#type-narrowing"><i class="material-icons">link</i></a></h3><p translation-result="on">在 <code><a href="api/common/NgIf" class="code-anchor">ngIf</a></code> 指令中使用的表达式用来在 Angular 模板编译器中窄化联合类型，就像 TypeScript 中的 <code>if</code> 表达式一样。 比如，要在上述模板中消除 <code>Object is possibly 'undefined'</code> 错误，可以把它改成只在 <code>person</code> 的值初始化过的时候才生成这个插值。</p><p translation-origin="off">The expression used in an <code><a href="api/common/NgIf" class="code-anchor">ngIf</a></code> directive is used to narrow type unions in the Angular template compiler, the same way the <code>if</code> expression does in TypeScript. For example, to avoid <code>Object is possibly 'undefined'</code> error in the template above, modify it to only emit the interpolation if the value of <code>person</code> is initialized as shown below:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">@<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'my-component', template: '&lt;span *<a href="api/common/NgIf" class="code-anchor">ngIf</a>="person"&gt; {{person.addresss.street}} &lt;/span&gt;' }) class MyComponent { person?: Person; }</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'my-component'</span><span class="pun">,</span><span class="pln">
  template</span><span class="pun">:</span><span class="pln"> </span><span class="str">'&lt;span *</span><a href="api/common/NgIf" class="code-anchor"><span class="str">ngIf</span></a><span class="str">="person"&gt; {{person.addresss.street}} &lt;/span&gt;'</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">class</span><span class="pln"> </span><span class="typ">MyComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  person</span><span class="pun">?:</span><span class="pln"> </span><span class="typ">Person</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">使用 <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> 能让 TypeScript 编译器推断出这个绑定表达式中使用的 <code>person</code> 永远不会是 <code>undefined</code>。</p><p translation-origin="off">Using <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> allows the TypeScript compiler to infer that the <code>person</code> used in the binding expression will never be <code>undefined</code>.</p><h4 id="custom-ngif-like-directives" translation-result="on">类似于的 <code><a href="api/common/NgIf" class="code-anchor">ngIf</a></code> 的自定义指令<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#custom-ngif-like-directives"><i class="material-icons">link</i></a></h4><h4 translation-origin="off" id="custom-ngif-like-directives">Custom <code><a href="api/common/NgIf" class="code-anchor">ngIf</a></code> like directives<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#custom-ngif-like-directives"><i class="material-icons">link</i></a></h4><p translation-result="on">那些行为与 <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> 类似的指令可以通过包含一个静态成员作为标记，来告诉模板编译器它们希望和 <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> 享受同等待遇。这个 <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> 的静态成员就是：</p><p translation-origin="off">Directives that behave like <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> can declare that they want the same treatment by including a static member marker that is a signal to the template compiler to treat them like <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code>. This static member for <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> is:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">public <a href="api/upgrade/static" class="code-anchor">static</a> ngIfUseIfTypeGuard: void;</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
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      </button>
      <code class="animated fadeIn"><span class="kwd">public</span><span class="pln"> </span><a href="api/upgrade/static" class="code-anchor"><span class="kwd">static</span></a><span class="pln"> ngIfUseIfTypeGuard</span><span class="pun">:</span><span class="pln"> </span><span class="kwd">void</span><span class="pun">;</span></code>
    </pre></aio-code></code-example><p translation-result="on">它声明了 <code><a href="api/common/NgIf" class="code-anchor">NgIf</a></code> 指令的 <code><a href="api/common/NgIf" class="code-anchor">ngIf</a></code> 属性应该在用到它的模板中看做一个守卫，以表明只有当 <code><a href="api/common/NgIf" class="code-anchor">ngIf</a></code> 这个输入属性为 <code>true</code> 时，才应该生成那个模板。</p><p translation-origin="off">This declares that the input property <code><a href="api/common/NgIf" class="code-anchor">ngIf</a></code> of the <code><a href="api/common/NgIf" class="code-anchor">NgIf</a></code> directive should be treated as a guard to the use of its template, implying that the template will only be instantiated if the <code><a href="api/common/NgIf" class="code-anchor">ngIf</a></code> input property is true.</p><h3 id="non-null-type-assertion-operator" translation-result="on">非空类型断言操作符<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#non-null-type-assertion-operator"><i class="material-icons">link</i></a></h3><h3 translation-origin="off" id="non-null-type-assertion-operator">Non-null type assertion operator<a title="Link to this heading" class="header-link" aria-hidden="true" href="guide/aot-compiler#non-null-type-assertion-operator"><i class="material-icons">link</i></a></h3><p translation-result="on">使用 <a href="guide/template-syntax#non-null-assertion-operator">非空类型断言操作符</a>可以在不方便使用 <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> 或 当组件中的某些约束可以确保这个绑定表达式在求值时永远不会为空时，防止出现 <code>Object is possibly 'undefined'</code> 错误。</p><p translation-origin="off">Use the <a href="guide/template-syntax#non-null-assertion-operator">non-null type assertion operator</a> to suppress the <code>Object is possibly 'undefined'</code> error when it is inconvenient to use <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> or when some constraint in the component ensures that the expression is always non-null when the binding expression is interpolated.</p><p translation-result="on">在下列例子中，<code>person</code> 和 <code>address</code> 属性总是一起出现的，如果 <code>person</code> 非空，则 <code>address</code> 也一定非空。没有一种简便的写法可以向 TypeScript 和模板编译器描述这种约束。但是这个例子中使用 <code>address!.street</code> 避免了报错。</p><p translation-origin="off">In the following example, the <code>person</code> and <code>address</code> properties are always set together, implying that <code>address</code> is always non-null if <code>person</code> is non-null. There is no convenient way to describe this constraint to TypeScript and the template compiler, but the error is suppressed in the example by using <code>address!.street</code>.</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">@<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'my-component', template: '&lt;span *<a href="api/common/NgIf" class="code-anchor">ngIf</a>="person"&gt; {{person.name}} lives on {{address!.street}} &lt;/span&gt;' }) class MyComponent { person?: Person; address?: Address; setData(person: Person, address: Address) { this.person = person; this.address = address; } }</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'my-component'</span><span class="pun">,</span><span class="pln">
  template</span><span class="pun">:</span><span class="pln"> </span><span class="str">'&lt;span *</span><a href="api/common/NgIf" class="code-anchor"><span class="str">ngIf</span></a><span class="str">="person"&gt; {{person.name}} lives on {{address!.street}} &lt;/span&gt;'</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">class</span><span class="pln"> </span><span class="typ">MyComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  person</span><span class="pun">?:</span><span class="pln"> </span><span class="typ">Person</span><span class="pun">;</span><span class="pln">
  address</span><span class="pun">?:</span><span class="pln"> </span><span class="typ">Address</span><span class="pun">;</span><span class="pln">

  setData</span><span class="pun">(</span><span class="pln">person</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Person</span><span class="pun">,</span><span class="pln"> address</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Address</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">person </span><span class="pun">=</span><span class="pln"> person</span><span class="pun">;</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">address </span><span class="pun">=</span><span class="pln"> address</span><span class="pun">;</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example><p translation-result="on">应该保守点使用非空断言操作符，因为将来对组件的重构可能会破坏这个约束。</p><p translation-origin="off">The non-null assertion operator should be used sparingly as refactoring of the component might break this constraint.</p><p translation-result="on">这个例子中，更建议在 <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code> 中包含对 <code>address</code> 的检查，代码如下：</p><p translation-origin="off">In this example it is recommended to include the checking of <code>address</code> in the <code>*<a href="api/common/NgIf" class="code-anchor">ngIf</a></code>as shown below:</p><code-example language="typescript" ng-version="9.0.0-rc.11"><div style="display:none">@<a href="api/core/Component" class="code-anchor">Component</a>({ selector: 'my-component', template: '&lt;span *<a href="api/common/NgIf" class="code-anchor">ngIf</a>="person &amp;&amp; address"&gt; {{person.name}} lives on {{address.street}} &lt;/span&gt;' }) class MyComponent { person?: Person; address?: Address; setData(person: Person, address: Address) { this.person = person; this.address = address; } }</div><aio-code><pre class="lang-typescript prettyprint">      <button title="Copy code snippet" class="material-icons copy-button no-print ng-star-inserted" aria-label="">
        <span aria-hidden="true">content_copy</span>
      </button>
      <code class="animated fadeIn"><span class="lit">@</span><a href="api/core/Component" class="code-anchor"><span class="lit">Component</span></a><span class="pun">({</span><span class="pln">
  selector</span><span class="pun">:</span><span class="pln"> </span><span class="str">'my-component'</span><span class="pun">,</span><span class="pln">
  template</span><span class="pun">:</span><span class="pln"> </span><span class="str">'&lt;span *</span><a href="api/common/NgIf" class="code-anchor"><span class="str">ngIf</span></a><span class="str">="person &amp;&amp; address"&gt; {{person.name}} lives on {{address.street}} &lt;/span&gt;'</span><span class="pln">
</span><span class="pun">})</span><span class="pln">
</span><span class="kwd">class</span><span class="pln"> </span><span class="typ">MyComponent</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
  person</span><span class="pun">?:</span><span class="pln"> </span><span class="typ">Person</span><span class="pun">;</span><span class="pln">
  address</span><span class="pun">?:</span><span class="pln"> </span><span class="typ">Address</span><span class="pun">;</span><span class="pln">

  setData</span><span class="pun">(</span><span class="pln">person</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Person</span><span class="pun">,</span><span class="pln"> address</span><span class="pun">:</span><span class="pln"> </span><span class="typ">Address</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">person </span><span class="pun">=</span><span class="pln"> person</span><span class="pun">;</span><span class="pln">
    </span><span class="kwd">this</span><span class="pun">.</span><span class="pln">address </span><span class="pun">=</span><span class="pln"> address</span><span class="pun">;</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span></code>
    </pre></aio-code></code-example></div></div></aio-doc-viewer></main></mat-sidenav-content></mat-sidenav-container><div class="toc-container no-print ng-star-inserted"><aio-lazy-ce selector="aio-toc"><aio-toc ng-version="9.0.0-rc.11"><div class="toc-inner no-print collapsed ng-star-inserted"><ul class="toc-list"><li class="h1 ng-star-inserted active" title="预先（AOT）编译器"><a href="guide/aot-compiler#ahead-of-time-aot-compilation">预先（AOT）编译器</a></li><li class="h2 ng-star-inserted" title="选择编译器"><a href="guide/aot-compiler#choosing-a-compiler">选择编译器</a></li><li class="h2 ng-star-inserted" title="AOT 工作原理"><a href="guide/aot-compiler#how-aot-works">AOT 工作原理</a></li><li class="h3 ng-star-inserted" title="编译的各个阶段"><a href="guide/aot-compiler#compilation-phases">编译的各个阶段</a></li><li class="h3 ng-star-inserted" title="元数据的限制"><a href="guide/aot-compiler#metadata-restrictions">元数据的限制</a></li><li class="h3 ng-star-inserted" title="配置 AOT 编译"><a 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